Hydrogen/hydrogen peroxide fuel cell

ABSTRACT

One embodiment of the present invention includes a technique of performing a catalytic oxidation reaction at an anode to provide hydrogen ions from molecular hydrogen and a catalytic reduction reaction at a cathode to provide hydroxyl ions from liquid hydrogen peroxide. Passage of the molecular hydrogen to a reaction region is impeded with a proton exchange membrane and passage of the hydrogen peroxide to the reaction region is impeded with an ion-selective arrangement. Electric potential is generated between the anode and the cathode to provide electric power from a reaction of the hydrogen ions and the hydroxyl ions in the reaction region. In one variation, a regeneration technique is also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 10/990,695 Nov. 17, 2004 (now U.S. Pat. No. 7,241,521), whichclaims the benefit of U.S. Provisional Patent Application No. 60/520,899filed Nov. 18, 2003. U.S. Provisional Patent Application No. 60/520,899filed Nov. 18, 2003 and U.S. application Ser. No. 10/990,695 filed Nov.17, 2004 (now U.S. Pat. No. 7,241,521)are each hereby incorporated byreference in their entirety.

BACKGROUND

The present invention relates to fuel cells, and more particularly, butnot exclusively relates to electrochemical fuel cells for whichreduction reactions occur at the cathode side using hydrogen peroxide.This reduction process, when combined with the oxidization reaction atthe anode side, generates electrical energy.

Aluminum-hydrogen peroxide (Al/H₂O₂) semi fuel cells have been studiedfor underwater propulsion. The existing problem with the Al/H₂O₂ semifuel cell is that the energy density is still lower than desired formany applications—particularly space propulsion implementations. Whilehydrogen peroxide H₂O₂ is used indirectly to generate oxygen gas forutilization at the cathode, there are significant difficulties fromdoing so. For example, in a fuel cell using air or oxygen on the cathodeside, the oxygen joins the reduction reaction in a gaseous form. Becausethe mass density achievable in this gas phase is ordinarily a thousandtimes less than that available in a liquid phase, the area currentdensity is at least 100 times less from this limiting factor alone. Toaddress this issue, ordinary fuel cells typically use a compressor topressurize the air/O₂ to a few Bars. Even so, the current density isstill at least 30 times less than the liquid phase counterpart. Theadditional weight and energy requirement of the pressurizing system alsorepresent performance penalties.

Furthermore, the mass transport of the reactants in such fuel cells is atwo-phase process. In a proton exchange membrane fuel cell inparticular, the two-phase transport of reactant and product species canbe a limiting phenomenon of fuel cell operation. Particularly, at highcurrent densities, transport of oxygen to the catalyst affects theoxygen reduction reaction rate in the cathode. Furthermore, the watergenerated in cathode reaction condenses when water vapor exceeds thesaturation pressure, and blocks the open pores of the gas diffusionlayer, further limiting reactant transport.

The slow kinetics of oxygen reduction has also been identified as afactor limiting the current density and the overall energy conversionefficiency of an oxygen fuel cell system. The oxygen reduction reactionat the cathode is written as: O₂+4 H⁺+4 e→2 H₂O. This reaction involvesfour electrons simultaneously, and therefore has a low probability ofoccurrence. Alternatively the poor kinetics of the oxygen reductionreaction can also be attributed to the low exchange current density ofthe oxygen reduction reaction. The high cathodic overpotential loss of220 mV, at potentials close to the open circuit, observed in the currentlow Pt loading electrocatalyst, is due to a mixed potential that is setup at the oxygen electrode. This mixed potential is from a combinationof slow O₂-reduction kinetics and competing anodic processes such asPt-oxide formation and/or impurity oxidation. Further, the low exchangecurrent density of the O₂-reduction reaction results in asemi-exponential, Tafel-like behavior—indicating that the reaction isactivation controlled over a range of three orders of magnitude incurrent density. It has been found that the exchange current density ofO₂-reduction is 6 orders of magnitude lower than that of H₂-oxidationreaction. Thus, there are numerous limitations associated with oxygengas reduction at a fuel cell cathode.

Accordingly, there is a need for further contributions in this area oftechnology.

SUMMARY

One embodiment of the present invention is a unique fuel cell. Otherembodiments include unique apparatus, methods, devices, and systemsrelating to fuel cells.

A further embodiment includes: performing an oxidation reaction at ananode to convert molecular hydrogen to hydrogen ions and a reductionreaction at a cathode to convert liquid hydrogen peroxide to hydroxylions, impeding passage of the molecular hydrogen to a reaction regionrelative to hydrogen ions, and impeding passage of the hydrogen peroxideto the reaction region relative to the hydroxyl ions. An electricpotential is generated between the anode and the cathode to provideelectric power from a reaction of the hydrogen ions and the hydroxylions in the reaction region. In one form, the oxidation reaction and/orreduction reaction are catalytic. Alternatively or additionally, thepassage of the molecular hydrogen is impeded by a proton exchangemembrane and/or the passage of the hydrogen peroxide is impeded by anion-selective arrangement.

In yet a further embodiment, an apparatus includes a source to supplymolecular hydrogen, a source to supply hydrogen peroxide, and a fuelcell. The fuel cell comprises: an anode subassembly coupled to the firstsource that includes an anode with one catalyst and a proton exchangemembrane to convert at least a portion of the molecular hydrogen fromthe first source into hydrogen ions, a cathode subassembly coupled tothe source of hydrogen peroxide that includes a cathode with a anothercatalyst and an ion-selective arrangement to convert at least a portionof the hydrogen peroxide from the second source into hydroxyl ions, anda reaction region separating the anode subassembly and the cathodesubassembly and being positioned between the proton exchange membraneand the ion selective-arrangement to receive hydrogen ions from theanode subassembly and hydroxyl ions from the cathode subassembly.

For one nonlimiting form of this apparatus, the fuel cell is effectiveto generate an electric potential between the anode and the cathode toprovide electrical power by reaction of the hydrogen ions and thehydroxyl ions when in the reaction region, the proton exchange membraneis selective to the passage of hydrogen ions therethrough relative tomolecular hydrogen, the ion-selective arrangement includes anion-selective membrane and a molecular sieve layer, and/or theion-selective membrane is selective to the passage of hydroxyl ionsrelative to hydrogen peroxide molecules.

Still another embodiment includes: performing a catalytic oxidationreaction at an anode to convert a hydride to hydrogen ions, impedingpassage of the hydride to a cathode relative to the hydrogen ions with aproton exchange membrane, performing a catalytic reduction reaction at acathode to convert hydrogen peroxide to hydroxyl ions, and reacting thehydrogen ions and the hydroxyl ions to provide electricity. Optionally,this embodiment may further include another anode to provide regeneratedhydride when an appropriate electric potential is placed across bothanodes and/or another cathode to provide regenerated hydrogen peroxidewhen another appropriate electric potential is placed across bothcathodes.

In yet another embodiment, a fuel cell includes: a discharge anode witha first catalyst to convert at least a portion of a source material intohydrogen ions, a discharge cathode with a second catalyst to converthydrogen peroxide into hydroxyl ions, a proton exchange membraneseparating the discharge anode and cathode that is selective to passageof hydrogen ions relative to the hydride to facilitate performance of areaction between the hydrogen ions and the hydroxyl ions to produceelectricity. The fuel cell further includes a regeneration negativeelectrode coupled with a third catalyst to provide regenerated sourcematerial when a selected electric potential is applied between thedischarge anode and the regeneration negative electrode. Alternativelyor additionally, the fuel cell further includes a regeneration positiveelectrode with a fourth catalyst to provide regenerated hydrogenperoxide when a suitable electric potential is applied between thedischarge cathode and the regeneration positive electrode. In oneparticular nonlimiting form, the source material includes a hydride fromwhich the hydrogen ions are generated.

Another embodiment comprises: discharging electricity from a fuel cellby performing a first catalytic oxidation reaction with a dischargeanode of the fuel cell to generate hydrogen ions from a source material,passing at least a portion of the hydrogen ions through a protonexchange membrane of the fuel cell, performing a first catalyticreduction reaction with a discharge cathode of the fuel cell to generatehydroxyl ions from hydrogen peroxide, and performing a reaction with thehydrogen ions and the hydroxyl ions to generate an electric potentialbetween the discharge anode and the discharge cathode to provide theelectricity; and recharging the fuel cell by performing at least one of:(a) applying an electric potential to a regeneration negative electrodeof the fuel cell to provide a second catalytic reduction reaction forregeneration of source material and (b) applying an electric potentialto a regeneration positive electrode of the fuel cell to provide asecond catalytic oxidation reaction for regeneration of hydrogenperoxide.

Accordingly, one object of the present invention is to provide a uniquefuel cell.

Another object of the present invention is to provide a uniqueapparatus, method, device, or system relating to fuel cells.

Further objects, embodiments, forms, aspects, benefits, advantages, andfeatures shall become apparent from the figures and description providedherewith.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective, partially schematic view of a fuel cell devicewhere a reaction region separates anode and cathode subassemblies.

FIG. 2 is a schematic block diagram of a power generation system thatutilizes at least one of the fuel cell devices of FIG. 1.

FIG. 3 is a perspective view of another fuel cell device.

FIG. 4 is a perspective, exploded view of a fuel cell device assemblycorresponding to the fuel cell device of FIG. 3.

FIG. 5 is a partial sectional view of the fuel cell assembly of FIG. 4taken along the view line 5-5 shown in FIG. 4.

FIG. 6 is a schematic block diagram view of a fuel cell system thatincludes yet another fuel cell device that is regenerative.

FIG. 7 is partial sectional view of the regenerative fuel cell deviceshown in FIG. 6.

FIG. 8 is a block diagram of a fuel cell system including a number ofthe fuel cell devices shown in FIGS. 6 and 7.

FIG. 9 is a diagrammatic view of a submersible underwater vehicle withthe system of FIG. 8 to provide electrical power.

FIG. 10 is a diagrammatic view of a spacecraft with the system of FIG. 8to provide electrical power.

DETAILED DESCRIPTION

While the present invention may be embodied in many different forms, forthe purpose of promoting an understanding of the principles of thepresent invention, reference will now be made to the embodimentsillustrated in the drawings, and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is thereby intended. Any alterations andfurther modifications in the described embodiments and any furtherapplications of the principles of the present invention as describedherein are contemplated as would normally occur to one skilled in theart to which the invention relates.

One embodiment of the present application is directed to providing ahydrogen/hydrogen peroxide (H₂/H₂O₂) fuel cell that uses H₂O₂ directlyat the cathode, rather than oxygen gas. Under certain circumstances,this unique technique can reduce energy loss and weight penalty comparedto other schemes based on the catalytic decomposition of H₂O₂. In oneform, the fuel cell is implemented in an air-independent applicationand/or, the hydrogen gas (H₂) is provided with a water/hydridereactant-based generator. Another embodiment of the present applicationis directed to a fuel cell that oxidizes hydride directly at the anodeinstead of hydrogen. One nonlimiting form of this embodiment is aNaBH₄/H₂O₂ fuel cell.

FIG. 1 depicts another embodiment of the present application in the formof H₂/H₂O₂ fuel cell device 20. Fuel cell device 20 includes fuel cell23 that has anode subassembly 30 opposite cathode subassembly 40, bothsubassemblies being separated by reaction region 24. Anode subassembly30 includes a porous anode 31 that includes oxidation catalyst 32, suchas platinum (Pt) or a compound/alloy including Pt, to name just a fewexamples. Anode subassembly 30 also includes Proton Exchange Membrane(PEM) 33 disposed proximate to anode 31. Anode 31 receives hydrogen gas(H₂) in molecular form for oxidation at anode 31 to produce protons(H⁺), and correspondingly provides such protons to reaction region 24through PEM 33. One or more hydrides can be used to generate this H₂ gasby reacting such hydrides with water, as is more fully describedhereinafter.

Cathode subassembly 40 includes porous cathode 41 that includesreduction catalyst 42, which can be iron (Fe), palladium (Pd), or acompound/alloy including Fe and/or Pd, to name just a few examples.Cathode subassembly 40 also has ion-selective arrangement 43 thatincludes molecular sieve layer 45 and ion-selective membrane 44.Molecular sieve layer 45 is positioned between cathode 41 andion-selective membrane 44, and is arranged to present a barrier tohydrogen peroxide molecules, while permitting passage of hydroxyl ions.Ion-selective membrane 44 provides hydroxyl ions (OH⁻) to reactionregion 24 through sieve layer 45. In reaction region 24, the protons(H⁺) from anode subassembly 30 and the hydroxyl ions (OH⁻) from cathodesubassembly 40 combine to provide water. Cell devices 20 can includevalves, metering controls, and/or sensors to regulate operation thereofas more fully described hereinafter.

For fuel cell device 20, the hydrogen peroxide (H₂O₂) is directly usedin cathode 41. This technique is in contrast to schemes in which H₂O₂was first decomposed and then the resulting O₂ gas was utilized in aH₂/O₂ fuel cell. By utilizing this liquid phase reactant, significantlygreater efficiencies can be realized compared to standard oxygengas-based fuel cells. At cathode 41, the hydrogen peroxide is reducedaccording to the reaction: H₂O₂+2 e→2 OH⁻. Compared to oxygen gasreduction, this hydrogen peroxide reduction is a two-electron transferprocess rather than a 4-electron transfer process, and involves a muchlower activation barrier. Furthermore, the arrangement of fuel cell 23at least partially compensates for loss due to the overpotential basedon the direct cathodic reduction of oxygen gas.

Referring additionally to FIG. 2, a power generation system 60 isillustrated that includes one or more of fuel cell devices 20; wherelike reference numerals refer to like features previously described inconnection with FIG. 1. System 60 further includes source 21 to supplymolecular hydrogen gas (an oxidation source material) and source 22 tosupply hydrogen peroxide (a reduction source material). Source 21 may bearranged to provide molecular hydrogen in a selected phase (such as agas or liquid) and/or comprise a hydrogen gas generator.

Source 21 is in fluid communication with anode subassembly 30.Correspondingly, source 21 can directly supply molecular hydrogen gas tosubassembly 30 and/or indirectly supply molecular hydrogen by reactionof a source material for a hydrogen gas generator form. By way ofnonlimiting example, a hydrogen gas generator form of source 21 provideshydrogen gas by reacting a metallic hydride with water, such that thehydride is the source material from which hydrogen is provided. In onespecific instance, a hydrogen gas generator is based on the reaction:2H₂O+MgH₂═Mg(OH)₂+H₂. Source 21 can include valves, metering controls,and/or sensors to regulate the supply/generation of hydrogen for the oneor more fuel cell devices 20 as appropriate.

Regardless of type of source, the molecular hydrogen gas from source 21is supplied to one or more fuel cell devices 20. Further, source 22 isin fluid communication with cathode subassembly 40 of each of the one ormore fuel cell devices 20 to supply hydrogen peroxide thereto in liquidform. Water management subsystem 70 is in fluid communication with oneor more fuel cells devices 20 to receive water produced by the one ormore devices 20 during operation. Appropriate valves, metering controls,and/or sensors to regulate the supply of hydrogen peroxide and water canbe included in source 22 and/or water management subsystem 70,respectively. Also, it should be appreciated that some or all of thewater utilized in source 21 to generate hydrogen gas can be providedfrom water management subsystem 70.

Referring to FIGS. 1 and 2 generally, operation of device 20 and system60 is next described. Hydrogen gas is processed by catalytic reaction atanode subassembly 30 of device 20 to provide protons, and hydrogenperoxide is processed by catalytic reaction at cathode subassembly 40 toprovide hydroxyl ions. The resulting protons from anode 31 pass throughPEM 33 to reaction region 24, and the resulting hydroxyl ions fromcathode 41 pass through sieve 45 and ion-selective membrane 44 toreaction region 24. In reaction region 24, the protons and hydroxyl ionsreact by combining to form water. Correspondingly, an electric potentialdevelops across anode 31 and cathode 41, which can be applied to anelectrical load 80 to provide electricity therefor.

In one embodiment, system 60 and/or device 20 is provided in aspacecraft. In another embodiment, system 60 and/or device 20 isincluded in a submersible underwater vehicle. In still otherembodiments, system 60 and/or device 20 is utilized in one or moredifferent “air-independent” applications; where “air independent”applications are those based on reactions that do not rely on air toprovide one or more reactants, such as oxygen. Yet other embodimentsutilize system 60 and/or device 20 with or without air-independence.

Fuel cell device 20 shown in FIG. 1 has independent molecular sievelayer 45 and ion-selective membrane 44 to reduce cross-over of hydrogenperoxide to anode subassembly 30. For some applications, a differentgeometry and/or structure of a H₂/H₂O₂ fuel cell may be desired. Forexample, in practice a fuel cell typically is structured as a stack offuel cells to generate a desired electrical output, which often favors athin, compact fuel cell construction that can be readily stackedtogether.

FIG. 3 depicts an exploded perspective view of one type of compact fuelcell device 120. Fuel cell device 120 includes fuel cell 121 that hasporous anode 130 and porous cathode 132. Cathode 132 is hydrophilicallytreated to attract water produced by the electrochemical reaction.Proton exchange membrane 134 separates anode 130 and cathode 132. Anode130 includes oxidation catalyst 131, such as any of those previouslydescribed. Anode 130 receives hydrogen gas (H₂) in molecular form foroxidation, and correspondingly provides protons (H⁺) through PEM 134.One or more metallic hydrides can be used to generate H₂ gas by reactingsuch hydrides with water, as previously explained.

Cathode 132 includes reduction catalyst 133, such as any of thosepreviously described. Proton exchange membrane 134 includes molecularsieve element 135, which presents a barrier to hydrogen peroxidemolecules. In one embodiment of PEM 134 with molecular sieve element135, Nafion (a perfluorinated sulfonic acid polymer) is utilized thathas a number of microporous water channels with size on the scale oftens of nanometers. Another PEM comprises an aromatic polyimide polymer.By mixing a suitable amount of nanoscale molecular sieve powder withNafion solution in a PEM casting process, the molecular sieve (MS)particles precipitate into the PEM water channel. When used in peroxidefuel cells, the MS particles act as a barrier against peroxidecross-over.

Continuing with FIG. 3, operation of device 120 is next described.Hydrogen gas is catalytically processed at anode 130 of device 120 toprovide protons through PEM 134, and hydrogen peroxide is catalyticallyreduced at cathode 132 to react with such protons to provide anelectrical potential between anode 130 and cathode 132. Anode 130 andcathode 132 can be coupled across an electrical load to provideelectricity thereto. For the depicted arrangement of device 120,reaction tends to predominantly occur nearest cathode 132 because of itshydrophilic treatment, so that an ion-selective membrane is nottypically required.

It should be appreciated that FIG. 3 shows fuel cell device 120 in aschematic form to enhance understanding of its features and operation.Referring additionally to FIGS. 4 and 5, one implementation of device120 is depicted as fuel cell assembly 125. Assembly 125 is relativelythin and compact, and is arranged to be stacked with a number of likeunits to collectively provide a desired electric power source. FIG. 4provides an exploded view of assembly 125, and FIG. 5 provides across-sectional view after assembling device 120 to provide assembly125. This sectional view corresponds to section line 5-5 depicted inFIG. 4.

As shown in FIGS. 4 and 5, anode 130 and cathode 132 of device 120 areattached (e.g., by hot pressing) to PEM 134 to collectively formMembrane Electrode Assembly (MEA) 122. Anode flow field plate 150 andcathode flow field plate 152 are positioned on opposite sides of the MEA122 to make electrical contact therewith. Plates 150 and 152 eachcontain respective grooves 151 and 153, on corresponding inner platefaces 151 a and 153 a. Grooves 151 of face 151 a are not visible in theperspective view of FIG. 4. As best illustrated in FIG. 5, when plates150 and 152 are assembled on opposing sides of MEA 122, grooves 151 and153 are disposed to form channels 161 through which reactants circulateand flow to make fluid contact with anode 130 and cathode 132(collectively electrodes ) of MEA 122.

Yet another embodiment of the present invention is directed to providinga hydride directly in an anode in a hydride/H₂O₂ fuel cell arrangement.In a preferred example, a NaBH₄/H₂O₂ fuel cell uses NaBH₄ directly inthe anode, rather than hydrogen gas. For this example, it should benoted that NaBH₄ is generally soluble in water so it can be supplied foroxidation by an anode in aqueous solution. Correspondingly, both fueland the oxidizer are subject to reaction in the liquid phase. Undercertain circumstances, this unique technique can reduce energy loss andweight penalty compared to other gas-based fuel cell arrangements.

Generally, this liquid/liquid fuel cell arrangement can be implementedwith device 120 and assembly 125 previously described. For a fuel cell120 and corresponding assembly 125 based on NaBH₄/H₂O₂ in particular,one embodiment prepares anode 130 from a porous carbon paste mixed witha powder form of an appropriate catalyst, such as platinum (Pt) or acompound/alloy including Pt, to name just a few examples. Further, anode130 for this embodiment is also hydrophilic-treated so that the aqueoussolution including NaBH₄ can permeate PEM 134. For arrangements of thiskind, the balanced pressure and matched mass density at the anode andcathode can reduce the reactant cross-over. At the anode, the reactionproceeds according to: NaBH₄+2 H₂O→NaBO₂+8 H⁺+8 e. The protons thentransfer through the PEM and react with the peroxide at the cathodeaccording to H₂O₂+2 H⁺+2 e→2 H₂O.

In a further embodiment of the present application, a 4-electrode“tetrode” fuel cell is illustrated in fuel cell system 210 of FIG. 6.For this arrangement, it has been found that regeneration of a fuel cellcan be enhanced under certain circumstances by providing a regenerationnegative electrode and cathode of different materials compared to thematerials used to make the discharge anode and cathode, respectively.For a NaBH₄/H₂O₂ type of fuel cell, the regeneration reaction typicallydesired is: NaBO₂+6H₂O→NaBH₄+4H₂O₂, with a thermodynamic potential ofabout 2.2V. From a theoretical standpoint, regeneration based on thisreaction is less likely to occur than undesired oxygen/hydrogenevolution reactions, such as: 2H₂O→2H₂+O₂, (thermodynamic potential ofabout 1.23V) because the desired regeneration reaction has a higherthermodynamic potential (2.2V>1.23V). However, it has been found thatelectrochemical reactions involving gas evolution can haveover-potentials dependent on the electrode material. Correspondingly,the applied voltage for the undesired reaction can be manipulated byelectrode material selection in at least some cases. For example, ahydrogen evolution reaction has an over-potential of 0V on a palladiummetal electrode but it is greater than 0.5V on an indium coatedelectrode. On the other hand, an oxygen evolution reaction has a smallover-potential of 0.3 V on an IrO₂ electrode but it increases to 0.6 Vfor a Pt metal electrode. For the NaBH₄/H₂O₂ type of fuel cell, thedischarge cathode (positive electrode in the fuel cell operation) can bemade of Pt or transition metal oxides (Ni(OH)₂ for example) while thedischarge anode (the negative electrode in the fuel cell operation) canbe made of Pt or PdO. For this selection of discharge electrodematerials, a regeneration (recharge) anode includes an indium coatingand the regeneration positive electrode includes a Pt or glassy carboncoated surface.

FIGS. 6 and 7 depict tetrode fuel cell device 220 directed to fuel celloperation of the NaBH₄/H₂O₂ type; where like reference numerals refer tolike features previously described. Device 220 includes fuel cell 224.Referring specifically to system 210 of FIG. 6, fuel cell 224 has porousdischarge anode 230 and porous discharge cathode 232 that are separatedby proton exchange membrane (PEM) 234. Discharge anode 230, dischargecathode 232, and PEM 234 are coupled together to form MEA 222. Anode 230is prepared from a porous carbon paste mixed with an oxidation catalyst231 in powder form. For this embodiment, catalyst 231 is platinum (Pt)or a compound/alloy including Pt; however, it can vary in otherembodiments. Anode 230 receives a hydride in aqueous solution foroxidation and correspondingly provides protons (H⁺) through PEM 234. Inone nonlimiting embodiment, the hydride is NaBH₄. Accordingly, for suchembodiments, anode 230 is hydrophilic-treated so an aqueous solution ofNaBH₄ can permeate it.

Cathode 232 includes reduction catalyst 233, Catalyst 233 is iron (Fe),palladium (Pd), or a compound/alloy including Fe and/or Pd; however, itcan vary in other embodiments. Proton exchange membrane 234 is preparedwith an integral molecular sieve element 235 like PEM 134 with element135, as described in connection with FIG. 3, which in turn is combinedwith anode 230 and cathode 232 to provide MEA 222. This integralmolecular sieve arrangement presents a barrier to hydrogen peroxidemolecules. Device 220 can include valves, metering controls, and/orsensors to regulate operation thereof as more fully describedhereinafter.

Fuel cell 224 further includes regeneration negative electrode 240 andregeneration positive electrode 242. Negative electrode 240 and positiveelectrode 242 are positioned on opposite sides of PEM 234 and areseparated from PEM 234 by anode 230 and cathode 232, respectively.Negative electrode 240 includes hydride regeneration catalyst 241.Catalyst 241 includes an indium (In) coating, but can vary in otherembodiments. Positive electrode 242 includes peroxide regenerationcatalyst 244. In one form, catalyst 244 includes platinum (Pt) or glassycarbon, but can vary in other embodiments.

It should be appreciated that FIG. 6 depicts device 220 in a schematicform to enhance understanding of its features and operation. FIG. 7illustrates a partial cross-section of one implementation of device 220as fuel cell assembly 225. This cross-sectional view corresponds to thesectional view of assembly 125 shown in FIG. 5, and otherwise mayexternally appear the same as assembly 125; however, there are internaldistinctions due to its tetrode configuration that shall become apparentfrom the following description. Correspondingly, assembly 225 can beprovided in a relatively compact form arranged for stacking with anumber of like units to provide a desired electric power source.

Referring to both FIGS. 6 and 7, anode 230 and cathode 232 are coupledon opposite sides of MEA 222 as a series of generally parallel electrodebars 251 a and 251 b, respectively. Bars 251 a and 251 b are separatedfrom one another by corresponding flow channels 261 a and 261 b. Bars251 a are electrically connected together in a standard manner toprovide anode 230, and bars 251 b are each electrically connectedtogether in a standard manner to provide cathode 232 (not shown in FIG.7). Flow channels 261 a facilitate the circulation of NaBH₄ in aqueoussolution for oxidation with anode 230, and flow channels 261 bfacilitate the circulation of H₂O₂ for reduction with cathode 232.

Anode 230 and cathode 232 are positioned between regeneration negativeelectrode 240 in the form of plate 240 a and regeneration positiveelectrode 242 in the form of plate 242 a. Accordingly, MEA 222 ispositioned between anode 230 and cathode 232, anode 230 is positionedbetween negative electrode 240 and MEA 222, cathode 232 is positionedbetween positive electrode 242 and MEA 222, and correspondingly each ofanode 230 and cathode 232 is positioned between negative electrode 240and positive electrode 242. Anode 230 is electrically insulated fromregeneration negative electrode 240 by insulation layer 245, andregeneration positive electrode 232 is electrically insulated fromcathode 242 by insulation layer 247. In one nonlimiting form, insulationlayer 245 and insulation layer 247 are formed from an electricallynonconductive epoxy; however, in other embodiments, a different type ofinsulation material could be utilized.

During operation of fuel cell device 220 (either discharge or recharge),catholyte containing hydrogen peroxide flows through channels 261 b, andanolyte containing NaBH₄ flows through channels 261 a. When dischargingdevice 220, anode 230 and cathode 232 provide negative and positivecontacts, respectively for electricity conduction through electricalload 280 as shown in FIG. 6. During discharge, regeneration negativeelectrode 240 and positive electrode 242 could be electrically floating(i.e., not electrically connected or grounded relative to the remainderof device 220). Alternatively, negative electrode 240 could beshort-circuited to anode 230 to reduce possible corrosion of indiumcoating during the discharge.

During recharge, recharge controller 290 provides an appropriateelectric potential across negative electrode 240 and positive electrode242 to regenerate hydrogen peroxide (catholyte) and NaBH₄ (anolyte). Thesurface of positive electrode 242 in contact with the catholytecomprises a high-O₂-over-potential material, which in this case is a Ptmetal or glassy carbon coating, while the surface of negative electrode240 in contact with the anolyte comprises a high-H₂-over-potentialmaterial, which in this case is an In metal coating. For an embodimentwith this material configuration, controller 290 can be configured toclamp the voltage between anode 230 and cathode 232 at about 1V duringrecharge. Also during recharge, it is desirable to control the potentialof anode 230 and cathode 232 to: (a) reduce possible electrode corrosionand (b) facilitate the transport of protons through MEA 222.Accordingly, in one embodiment, controller 290 provides about a +0.7Vpotential difference between positive electrode 242 and cathode 232(positive electrode 242 being more positive than cathode 232) and abouta −0.7V potential difference between negative electrode 240 and anode230 (negative electrode 240 being more negative than anode 230). Itshould be appreciated that the catholyte, anolyte, and water need to bemanaged and routed during device 220 operation, both for discharge andrecharge, and that corresponding equipment of a standard type can beutilized for this purpose (not shown).

Referring additionally to FIG. 8, power generation system 320 isillustrated that includes a fuel cell stack 322 comprised of a number ofstacked fuel cell devices 220 (shown in FIGS. 6 and 7); where likereference numerals refer to like features of previously describedembodiments. System 320 further includes NaBH₄ supply 330, hydrogenperoxide supply 332, and water holding tank 334. Collectively, supply330, supply 332, and tank 334 provide supply and storage subsystem 340.Subsystem 340 is operatively coupled to discharge/recharge subsystem350. Subsystem 350 includes stack 322, radiator 352, radiator/separator354, electrical power control/regulation device 370, NaBH₄ circulator382, H₂O₂ circulator 384, and recharge controller 290.

Circulators 382 and 384 each include one or more pumps, conduits,valves, meter, or the like to function as described hereinafter. Supply330 includes a sodium borohydride (NaBH₄) storage tank and waterhandling/routing equipment coupled to water holding tank 334. As wateris generated by the fuel cell discharge reaction, it is controllablycirculated back to supply 330 and mixed with NaBH₄ to carry more of thecorresponding solution to stack 322 to sustain the discharge reaction.This NaBH₄ solution is routed from supply 330 to subsystem 350 by pump382. Supply 330 can include valves, metering controls, and/or sensors toregulate the supply, concentration, and/or pH value of the NaBH₄solution provided to subsystem 350, as appropriate.

Supply 332 is arranged with a tank that stores concentrated hydrogenperoxide as well as corresponding water handling/routing equipment. Inone nonlimiting example, a 60% hydrogen peroxide solution is utilized;however, other concentrations can be used in different embodiments.Water from the discharge reaction is circulated back to supply 332 withcirculator 384 to dilute the concentrated hydrogen peroxide. Circulator384 also is operable to provide the resulting H₂O₂/H₂O mixture fromsupply 332 to stack 322. Source 332 can include valves, meteringcontrols, and/or sensors to regulate the supply, concentration, and/orpH value of the peroxide solution provided to subsystem 350, asappropriate.

Radiator 352 and the radiator portion of radiator/separator 354 eacheject waste heat to the environment that is generated by fuel celloperation. Either or both could be in the form of a heat exchanger foran underwater application, a space radiator for a spacecraftapplication, or such different form suitable for the particularapplication as would occur to one skilled in the art.

During an electricity discharge operation of fuel cell devices 220 instack 322, sodium borohydride (NaBH₄) is catalytically processed at eachcorresponding discharge anode 230 and hydrogen peroxide is catalyticallyreduced at each corresponding discharge cathode 232 to provideelectrical energy to electrical load 360. The electrical voltage,current and/or power output to load 360 is regulated with powercontrol/regulator 370 during discharge. As the discharge reactionproceeds, it generates water at each discharge cathode 323, which iscarried away with the circulating hydrogen peroxide. The separatorportion of radiator/separator 354 separates at least a portion of thewater and provides it to tank 334 of subsystem 340 for reuse asappropriate.

As the fuel and/or oxidizer of system 320 is spent, a regeneration(recharge) operating mode can be engaged. In one embodiment, thecondition(s) triggering regeneration can be detected with controller390. Alternatively or additionally, such condition(s) can be detectedwith power controller/regulator 370, can be manually triggered, and/orsuch different arrangement could be used to change operating modes aswould occur to one skilled in the art. During recharge operation, foreach cell device 220, an electric potential difference is applied acrossregeneration negative electrode 240 and regeneration positive electrode242 with controller 390. In one nonlimiting example, the relativeelectric potentials and corresponding electrode materials could be thosedescribed for device 220 in connection with system 210 of FIG. 6. Inother examples, the applied recharge potential(s), electrode materials,cell configuration, or the like could be varied and/or may be directedto different fuel and/or oxidizer constituents.

As recharging progresses, sodium borohydride (NaBH₄) and hydrogenperoxide (H₂O₂) are regenerated, and are routed back to the respectivetanks of supplies 330 and 332 in an aqueous solution. Once a desiredrecharge level is reached, system 320 can return to a discharge mode ofoperation, as desired for the particular application. It should also beappreciated that in other embodiments, system 320 could vary by mixing,exchanging, or duplicating the various embodiments of fuel cellsdescribed herein. Alternatively or additionally, other embodiments mayvary in the particular fuel cell geometry or physical configuration, inthe type of fuel used, in the type of oxidizer used, in the type ofrecharge methodology/equipment used, and/or in the way reactants orreaction products are handled. In still other embodiments, a single fuelcell instead of a stack may be utilized and/or a recharge capability maybe absent.

Any of these fuel cell system embodiments and their variations could beused in various applications, including but not limited to thoseillustrated in FIGS. 9 and 10. Referring to FIG. 9, a further embodimentincludes system 320 in a submersible underwater vehicle 420 asillustrated therein. For this embodiment system 320 provides electricpower to vehicle 420. In another embodiment illustrated in FIG. 10,system 320 is included in spacecraft 410 to provide electric powerthereto. In still other embodiments, system 260 and/or device 220 areutilized in one or more different air independent applications. Yetother embodiments utilize system 260 and/or device 220 with or withoutair-independence.

One form of the present invention is a unique fuel cell. Other formsinclude unique methods, systems, devices, and apparatus involving fuelcells. Among these forms are methods, systems, devices, and apparatusdirected to a liquid/liquid type of fuel cell. For this liquid/liquidfuel cell type, a preferred embodiment includes hydrogen peroxide as areactant, a more preferred embodiment includes sodium borohydride andhydrogen peroxide as reactants. Yet other forms include methods,systems, devices, and apparatus directed to regenerative fuel cells. Forthis regenerative fuel cell type, one preferred embodiment includes oneor more regeneration electrodes in addition to two discharge electrodes,and a more preferred embodiment includes at least two regenerationelectrodes in addition to two discharge electrodes.

A further form includes a fuel cell with an anode subassembly and acathode subassembly. The anode subassembly includes an anode with one ormore catalysts to generate protons from molecular hydrogen and providethe protons through a proton exchange membrane. The cathode subassemblyincludes a cathode with one or more catalysts to generate hydroxyl ionsfrom hydrogen peroxide, and an ion-selective arrangement to provide thehydroxyl ions for reaction with protons from the proton exchangemembrane. The ion-selective arrangement can include a molecular sievelayer selective to hydroxyl ions and an ion-selective membrane, with thesieve layer being positioned between the cathode and the ion-selectivemembrane. Yet another form of the present invention includes a systemcomprising one or more of the fuel cells coupled to a hydrogen gassource and a hydrogen peroxide source, and an electrical loadoperatively coupled across the anode and cathode.

Another form includes oxidizing hydrogen at an anode and reducinghydrogen peroxide at a cathode to generate electrical power. Thehydrogen can be provided in gaseous form by reacting water and ametallic hydride. The hydrogen peroxide can be provided in a liquidform. The act of oxidizing hydrogen can be performed with an anodesubassembly comprising an anode and a proton exchange membrane. Theanode includes a catalyst to generate protons from the hydrogen.Alternatively or additionally, the act of reducing hydrogen peroxide canbe performed with a cathode subassembly comprising a cathode and anion-selective arrangement. In one form, the ion-selective arrangementincludes a molecular sieve layer and an ion-selective membrane tofacilitate selective passage of hydroxyl ions from the cathodesubassembly and separate hydrogen peroxide from the proton exchangemembrane. The anode subassembly and the cathode subassembly can beprovided in the form of a fuel cell.

In still another form, an H₂/H₂O₂ fuel cell is provided in which H₂ isoxidized at an anode while H₂O₂ is reduced at a cathode. The cell caninclude a proton exchange membrane as an electrolyte to conduct the H⁺ion (proton). When a proton exchange membrane is used, the H₂O₂ at thecathode is isolated from the proton exchange membrane by a layer ofmolecular sieve impervious to H₂O₂. This molecular sieve is permeable towater and to hydroxyl ions, and can be separated from the protonexchange membrane by an ion-selective membrane that is conductive tohydroxyl ions. A cathode of the cell can be made of one or more porousmaterials containing Fe, Pd, and/or one or more chemical compoundsincluding Fe and/or Pd.

All publications and patent applications cited in this specification areherein incorporated by reference as if each individual publication orpatent application were specifically and individually indicated to beincorporated by reference. Further, any theory, mechanism of operation,proof, or finding stated herein is meant to further enhanceunderstanding of the present invention, and is not intended to limit thepresent invention in any way to such theory, mechanism of operation,proof, or finding. While the invention has been illustrated anddescribed in detail in the drawings and foregoing description, the sameis to be considered as illustrative and not restrictive in character, itbeing understood that only selected embodiments have been shown anddescribed and that all equivalents, changes, and modifications that comewithin the spirit of the inventions as defined herein or by thefollowing claims are desired to be protected.

1. A method, comprising: providing a fuel cell including an anode, acathode, and an ion exchange membrane positioned therebetween;performing a first catalytic reaction at the anode to provide hydrogenions from a hydride in liquid solution; performing a second catalyticreaction at the cathode to provide hydroxyl ions from liquid phasehydrogen peroxide; at least partially maintaining separation of thehydride and hydrogen peroxide with the ion exchange membrane positionedbetween the anode and the cathode; permitting selective ion passagethrough the ion exchange membrane to form water molecules from thehydrogen ions and the hydroxyl ions; and as the water molecules formfrom the hydrogen ions and the hydroxyl ions, generating an electricpotential across the anode and the cathode to provide electric powerwith the fuel cell.
 2. The method of claim 1, wherein the hydride inliquid solution comprises a metallic hydride dissolved in water.
 3. Themethod of claim 1, wherein said ion exchange membrane further impedespassage of liquid hydrogen peroxide to the anode.
 4. The method of claim1, which includes: carrying the hydride in liquid solution, the liquidphase hydrogen peroxide, and the fuel cell with a spacecraft or asubmersible underwater vehicle; and from the fuel cell, providing theelectric power to the spacecraft or the submersible underwater vehicle.5. The method of claim 1, wherein the anode comprises a first plate withgrooves to receive an aqueous solution including at least part of thehydride and the cathode comprises a second plate with other grooves toreceive a flow of at least part of the hydrogen peroxide, the firstplate and the second plate being positioned opposite one another.
 6. Themethod of claim 1, which includes regenerating the fuel cell with anelectrical energy source coupled thereto.
 7. The method of claim 1,wherein at least one of the anode and the cathode comprise a porous,electrically conductive substrate.
 8. The method of claim 1, wherein thefirst catalyst comprises at least one of platinum, palladium, and analloy including one or more of platinum and palladium.
 9. The method ofclaim 1, wherein the second catalyst comprises at least one of iron,palladium, and an alloy including one or more of iron and palladium. 10.An apparatus, comprising: a first source to supply a hydride in liquidsolution; a second source to supply hydrogen peroxide in liquid phase; afuel cell, including: an anode subassembly in fluid communication withthe first source to receive the hydride, the anode subassembly includingan anode and a first catalyst to convert at least a portion of thehydride to hydrogen ions; a cathode subassembly in fluid communicationwith the second source to receive the hydrogen peroxide, the cathodesubassembly including a cathode and a second catalyst to convert atleast a portion of the hydrogen peroxide to hydroxyl ions; and anion-selective arrangement positioned between the anode and the cathodeto maintain separation of the hydride and hydrogen peroxide, theion-selective arrangement being structured to permit selective ionpassage therethrough to form water molecules from the hydrogen ions andthe hydroxyl ions, the fuel cell being effective to correspondinglygenerate an electrical potential across the anode and cathode to provideelectric power as the water molecules form.
 11. The apparatus of claim10, wherein the hydride comprises a metallic hydride.
 12. The apparatusof claim 10, wherein at least one of the anode and the cathode comprisea porous, electrically conductive substrate.
 13. The apparatus of claim10, wherein said first catalyst comprises at least one of platinum,palladium, and an alloy including one or more of platinum and palladium.14. The apparatus of claim 10, wherein said second catalyst comprises atleast one of iron, palladium, and an alloy including one or more of ironand palladium.
 15. The apparatus of claim 10, further comprising meansfor regenerating the fuel cell.
 16. The apparatus of claim 10, furthercomprising a spacecraft or a submersible underwater vehicle carrying thefirst source, the second source, and the fuel cell.
 17. The apparatus ofclaim 10, wherein the anode comprises a first plate with grooves toreceive an aqueous solution including at least part of the hydride andthe cathode comprises a second plate with other grooves to receive aflow of at least part of the hydrogen peroxide, the first plate and thesecond plate being positioned opposite one another.